A permanent magnet type electric motor (hereinafter, “permanent magnet motor”) employing an inverter drive system is known as a conventional electric motor serving as a rotating electrical machine for vehicles, which are used in electric vehicles or hybrid cars. The permanent magnet motor is constructed by a stator core on which stator coils are wound to constitute a plurality of phases, for example, three phases of U, V and W. The permanent magnet motor includes sheets of interphase insulation paper inserted between coil ends of the stator coils (between U and V phases, between V and W phases and the like; and hereinafter referred to as “between different phases”), so that the coil ends of the stator coils are prevented from contact with each other.
Each one of the stator coils includes a plurality of generally series-connected unit coils, and there is a possibility that coil ends of adjacent unit coils may be brought into contact with each other between the stator coils of the same phase (hereinafter referred to as “between the same phases”) as well as between different phases. For example, in the permanent magnet motor of the vehicle, a drive voltage has been rendered higher for the purposes of higher output. Furthermore, an inverter serge voltage having a steep rise by inverter drive is applied to the motor.